This invention relates to papermaking and more particularly to fabrics for use on a paper board papermaking machine.
Generally a papermaking machine comprises a forming section, a press section and a dryer section. Papermakers fabrics transport an aqueous paper web through the machine to produce the paper product. Each of the three sections of the papermaking machine has its own unique characteristics and requirements. Accordingly, papermakers fabrics are specifically designed for each section of the papermaking machine such as forming fabrics for the forming section, wet press felts for the press section and dryer fabrics for the dryer section.
In operation, an aqueous paper web is formed on a forming fabric as the fabric passes through a slurry of wood pulp the like and over suction boxes. The suction boxes remove water to impart a degree of structural integrity to the web. The web is then transferred from the forming fabric to wet press felts for transportation through the pressing section of the papermaking machine. Thereafter, the pressed paper web is transferred to dryer fabrics for transportation through the dryer section of the papermaking machine.
Some relatively specialized papermaking equipment, such as paper board making equipment, have hybrid sections where a single fabric is required for both forming and some of the pressing operations. In such machines, the fabrics must not only have the capacity to uniformly form the aqueous base material into a paper board web, but also must be able to transport the web through the nip of press rollers.
In the pressing operation, the aqueous paper board web, due to its high moisture content, is highly susceptible to marking if the transporting surface of the fabric is not completely uniform in its characteristics. Additionally, uniform permeability of the fabric is important to assure the uniform formation of the web as well as to provide for the uniform dewatering of the web as it passes over suction cylinders and through press nips.
One conventional way of achieving uniformity of the fabric is to weave the fabric endless. However, such fabrics tend to be more difficult to install on papermaking equipment and the equipment must be specifically designed structurally to be able to accept an endless fabric.
Alternatively, a seam may be incorporated into the fabric which enables one end of the fabric to be threaded through the machine and joined with its opposing end in site which can greatly facilitate installation of the fabric on the machine. However, the seam area must have substantially the same characteristics as the remainder of the fabric to assure uniform formation and to avoid marking of the paper board web.
Fabrics comprising a base fabric made from monofilament synthetic yarns having a fibrous batt needled thereto have been designed for use with paper board papermaking equipment. However, in order to maintain a uniform caliper throughout both the body and the seam area of the fabric, base fabrics of such seamed fabrics have been comprised of multiple layers of monofilament yarns.
Multi-layer fabrics can be constructed with intermeshing end loops which are equal to or within the top and bottom base fabric layers such as disclosed in U.S. Pat. No. 3,815,645. However, multi-ply base fabrics become problematic when trying to achieve the desired weight and permeability requirements using a multi-ply base fabric.
It is desirous to provide papermakers fabric having a single-layer seamed base fabric to facilitate the forming and pressing operations in the manufacture of paper board.